Amazing SAT Practice but not enough Question-Specific Material

Ինչպե՞ս կարող ենք օգնել:

Matthew Burgnon

August 04, 2017 01:29
Edited

I LOVE the SAT practice course. I often find myself digging up mistakes I've made and solving them to never see them again. That being said, when I run into a concept I've never learned, I struggle and find myself scouring the internet (and khan academy) to find the answer to my problem.

My most recent example of this is when I was working on the "Manipulating quadratic and exponential expressions" module and I ran into this problem:

Abhishek received an injection of a medication. The following expression shows the number of milligrams of medication left in his body after ttt hours.

37⋅0.25^(t/16)

Half-life of a medicine refers to the amount of time it takes for half of the medicine to leave the body. What is the half-life (in hours) of Abhishek's medicine?

After getting the problem wrong and reading how to solve it, I found myself confused and left still wondering why certain numbers were brought up in certain locations. Then, I looked at the videos and they apparently had nothing related to the problem I was attempting to solve (both easy and hard).

So I guess my suggestion would be to have more problem-type specific videos that can help someone like myself better learn the concepts behind some of the problems. Videos realyl are the best way I learn things so this really would help when it comes to preparing for the SAT.

Thanks for the great program and keep up the good work!

New post

1 comment

Pei-Hsin Lin 林培心 🌸

August 04, 2017 03:59

Edited
1

Comment actions Permalink
Hi Matthew,

For help with specific problems, just post your question and the Khan Academy community will try to help you. As for the question you have mentioned:

Medicine (M) in milligrams is given as a function of time (t) in hours as follows. What is the half-life of Abhishek's medicine?

M(t) = 37·(¼)^(t/₁₆)

Just reformat the function using exponent rules, so that ½ is the base instead of ¼.

The exponent of ½ will reveal the half-life!

37·(¼)^(t/₁₆) =

37·[(½)²]^(t/₁₆) =

37·½^(2·t/₁₆) =

37·½^(⅛t)

Now that the base is ½ and the exponent is t over 8, the equation makes clear that the amount of medicine gets halved again every time t reaches a multiple of 8.

At t = 0 hours, M = 37 mg

At t = 8 hours, M = 37·½ = 18.5 mg

At t = 16 hours, M = 37·½·½ = 9.25 mg

What's the half-life? 8 hours, of course!

For more practice problems like this, check out Khan Academy's Exponential model word problems section:

https://www.khanacademy.org/math/algebra2/exponential-and-logarithmic-functions/solving-exponential-models/e/exponential-models-word-problems

Post is closed for comments.

Amazing SAT Practice but not enough Question-Specific Material

Didn't find what you were looking for?

1 comment

Didn't find what you were looking for?